Avian influenza, sometimes avian flu, and commonly bird flu refers to influenza caused by viruses adapted to birds. Avian influenza virus (AIV) is an RNA virus belonging to the family of Orthomyxoviridae, and is classified as a type A influenza virus, which relates to its nucleoprotein and membrane proteins. AIV has a lipid envelope that features two distinct glycoproteins: hemagglutinin (HA), which facilitates entry of the virus into the host cells, and neuraminidase (NA), which assists in the release of progeny virus from infected cells (de Jong et al., J Clin Virol. 2006 January; 35(1):2-13). The H5N1 subtype (virus featuring HA 5 and NA 1) has specifically been associated with recent outbreaks in Asia, Russia, the Middle East, Europe and Africa (Olsen et al., Science. 2006 Apr. 21; 312(5772):384-8).
The highly pathogenic Influenza A virus subtype H5N1 virus is an emerging avian influenza virus that has been causing global concern as a potential pandemic threat. H5N1 has killed millions of poultry in a growing number of countries throughout Asia, Europe and Africa. Health experts are concerned that the co-existence of human flu viruses and avian flu viruses (especially H5N1) will provide an opportunity for genetic material to be exchanged between species-specific viruses, possibly creating a new virulent influenza strain that is easily transmissible and lethal to humans (Food Safety Research Information Office. “A Focus on Avian Influenza”. Created May 2006, Updated November 2007).
Since the first H5N1 outbreak occurred in 1997, there have been an increasing number of HPAI H5N1 bird-to-human transmissions leading to clinically severe and fatal human infections. However, because there is a significant species barrier that exists between birds and humans, the virus does not easily cross over to humans. Although millions of birds have become infected with the virus since its discovery, over 200 humans have died from Avian Flu in Indonesia, Laos, Vietnam, Romania, China, Turkey and Russia.
Recently, plants have been investigated as a source for the production of therapeutic agents such as vaccines, antibodies, and biopharmaceuticals. However, the production of vaccines, antibodies, proteins, and biopharmaceuticals from plants is far from a remedial process, and there are numerous obstacles that are commonly associated with such vaccine production. Limitations to successfully producing plant vaccines include low yield of the bioproduct or expressed antigen (Chargelegue et al., Trends in Plant Science 2001, 6, 495-496), protein instability, inconsistencies in product quality (Schillberg et al., Vaccine 2005, 23, 1764-1769), and insufficient capacity to produce viral-like products of expected size and immunogenicity (Arntzen et al., Vaccine 2005, 23, 1753-1756).
Considering the susceptibility of animals, including humans, to AIV, a method of preventing AIV infection and protecting animals is essential. Accordingly, there is a need for methods to produce effective vaccines against influenza.